Different types of acoustic devices have been used through the years. One type of device is a microphone. In many microelectromechanical system (MEMS) microphones, a MEMS die includes at least one diaphragm and at least one back plate. The MEMS die is supported by a substrate and enclosed by a housing (e.g., a cup or cover with walls). A port may extend through the substrate (for a bottom port device) or through the top of the housing (for a top port device). In any case, sound energy traverses through the port, moves the diaphragm and creates a changing potential of the back plate, which creates an electrical signal. Microphones are deployed in various types of devices such as personal computers or cellular phones.
Pressure sensors are also used to measure various types of pressures. Current microphones sometimes have a pierce in the diaphragm that allows for pressure equalization between the back volume and the ambient environment so that microphone sensitivity does not shift with changes in ambient pressure. This pierce is an acoustic high-pass filter making the microphone respond only to alternating current (AC) signals, while not responding to direct current (DC) or slowly varying (ambient pressure) signals. Thus, current microphones using this configuration do not generally include pressure sensors.
The problems of previous approaches have resulted in some user dissatisfaction with these previous approaches.